Process method for preparing sodium ferric sulfate composite positive electrode material from crystal water-free precursor and sodium ion battery

Abstract

The invention relates to the technical field of sodium ion battery positive electrode materials, and discloses a process method for preparing a sodium ferric sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery. The problems of low crystallinity of Na < 2 + > 2 < delta > Fe < 2-delta > (SO4) 3 and easy oxidation of Fe < 2 + > caused by water vapor generated when the Na2Fe (SO4) 2.4 H2O precursor is heated and hydrated are solved. On the basis, aiming at the defect of poor electronic conductivity of Na < 2 + 2 > < delta > Fe < 2-delta > (SO4) 3, the invention provides the Na < 2 + 2 > < delta > Fe < 2-delta > (SO4) 3 / C composite positive electrode material with improved conductivity, and the composite positive electrode material can show excellent high rate capacity and long cycle stability at room temperature and in high and low temperature environments, and has a relatively good prospect in the field of novel energy storage.

Description

Technical Field

[0001] The invention relates to a process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery, belonging to the technical field of sodium ion batteries. Background Art

[0002] New energy storage technologies can not only reduce dependence on fossil fuels and greenhouse gas emissions, but also improve the utilization efficiency and stability of renewable energy. The progress of new energy storage technologies can further promote the upgrading and development of related industries, create more jobs, and effectively drive economic growth. With its excellent cycle life and moderate energy density, lithium-ion batteries account for a much larger share of new energy storage fields than compressed air energy storage, flywheel energy storage, and supercapacitor energy storage. However, the safety hazards of lithium-ion batteries at high temperatures and the capacity decay at low temperatures cannot be ignored. Sodium-ion batteries (SIBs) are regarded as one of the strong competitors in the future large-scale energy storage market due to their similar energy storage mechanism to lithium-ion batteries, as well as their abundant Na element reserves, superior thermal safety, and less low-temperature capacity decay, especially energy storage devices used in extreme environments, such as photovoltaic power generation and storage facilities in high-temperature desert areas and wind power generation and storage facilities in high-altitude and low-temperature areas. Therefore, the development of sodium-ion batteries that can maintain stable performance over a wide temperature range has huge potential demand in the energy storage market. In this context, polyanion cathode materials have attracted extensive attention from researchers due to their low cost, wide temperature range stability, and long cycle stability. In particular, iron-based polyanionic sulfate sodium-ion battery cathode materials are considered to be one of the most promising materials for use in new energy storage fields.

[0003] Alluaudite type Na 2+2δ Fe 2-δ (SO4)3 material has been reported as a potential cathode material for sodium-ion batteries for energy storage due to its high operating voltage, long cycle life and low cost. However, its high sensitivity to moisture and oxygen during calcination causes the Fe in its crystal structure to 2+ Easily oxidized to Fe 3+ , resulting in low crystallinity of the product. Especially when using hydrated Na2Fe(SO4)2·4H2O precursor to prepare Na 2+2δ Fe 2-δ In the process of (SO4)3 cathode material, the water vapor produced by heating the crystallization water can easily reduce the Na 2+2δ Fe 2-δ The crystalline integrity of (SO4)3 and the easy formation of Fe 2+In addition, FeO6 and FeO6 in the crystal structure are connected by non-conductive SO4 groups, which makes it difficult for electrons to transfer during charge and discharge, resulting in insufficient high-rate capacity of the original material and rapid capacity decay. Summary of the invention

[0004] Based on this, the present invention provides a process for preparing a sodium iron sulfate composite positive electrode material from a precursor without crystal water, which avoids the Na 2+2δ Fe 2-δ (SO4)3 low crystallinity and Fe 2+ On this basis, a Na 2+2δ Fe 2-δ (SO4)3 / C composite positive electrode material not only shows high average working potential, superior high-rate capacity and excellent cycle stability at room temperature, but also has excellent cycle stability under extreme conditions of high and low temperatures, and has good prospects for use in new energy storage fields.

[0005] To achieve the above-mentioned purpose, the process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery described in the present invention can be implemented by the following technical scheme, which mainly includes the following steps:

[0006] Step 1: Preparation of crystal water-free precursor material

[0007] Sodium sulfate, ferrous sulfate and ascorbic acid are added to deionized water according to the molar ratio, and are continuously stirred to completely dissolve to obtain a transparent aqueous solution with uniformly dispersed solutes. Then, an appropriate amount of carbon nanotubes are added and ultrasonically dispersed to obtain a black suspension, and finally the black suspension is vacuum dried to obtain a precursor material without crystal water.

[0008] Step 2: Sintering preparation of sodium iron sulfate composite positive electrode material

[0009] The sodium iron sulfate composite positive electrode material can be obtained by sintering the precursor without crystal water in a tubular furnace with an inert atmosphere and then cooling it to room temperature.

[0010] Step 3: Preparation of sodium ion battery

[0011] The positive electrode material, conductive carbon black and binder are weighed and ground in a ball mill according to a mass fraction ratio of 70:20:10. Then the evenly ground slurry is scraped onto the aluminum foil current collector. After vacuum drying overnight, it is rolled and cut to obtain the positive electrode sheet. In a glove box filled with argon (water and oxygen content are both less than 0.1ppm), the positive electrode, diaphragm and negative electrode are assembled in order, and finally an appropriate amount of electrolyte (1M NaClO4 EC:PC=1:1 and 5vol%FEC) is injected and sealed to obtain a sodium ion battery.

[0012] Furthermore, in step 1, the molar ratio of the iron salt to ascorbic acid is 20-80:1.

[0013] Furthermore, in step 1, the material drying and crystallization process is under vacuum conditions, the vacuum drying temperature is 100-150° C., and the drying time is 12-24 hours.

[0014] Furthermore, in step 1, the amount of carbon nanotubes added is 1-10 wt.%.

[0015] Furthermore, in step 2, the inert atmosphere is at least one of Ar, N2, and Ar+H2.

[0016] Furthermore, in step 2, the sintering temperature is 350-450° C., and the sintering time is 6-12 hours.

[0017] Beneficial Effects

[0018] In the above technical scheme, the Na2Fe(SO4)2 precursor material without crystal water prepared by vacuum drying process will not release water vapor like the Na2Fe(SO4)2·4H2O hydrated precursor during the subsequent sintering process, thus avoiding the water vapor in the sintering process that easily causes Na 2+2δ Fe 2-δ (SO4)3 has low crystallinity and Fe 2+ On this basis, for Na 2+2δ Fe 2-δ (SO4)3 has the disadvantage of poor electronic conductivity, and provides a Na 2+2δ Fe 2-δ (SO4)3 / C composite positive electrode material, which can exhibit excellent high-rate capacity and long-cycle stability at room temperature and high and low temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0020] Figure 1This is the X-ray diffraction pattern of the prepared Na2Fe(SO4)2 precursor composite material without crystalline water.

[0021] Figure 2 This is the TG-DSC graph of the prepared Na2Fe(SO4)2 precursor composite material without crystal water.

[0022] Figure 3 The prepared Na 2+2δ Fe 2-δ X-ray diffraction pattern of (SO4)3 / C composite positive electrode material.

[0023] Figure 4 It is prepared Na 2+2δ Fe 2-δ Scanning electron microscope image of (SO4)3 / C composite positive electrode material.

[0024] Figure 5 is Na in Example 1 2+2δ Fe 2-δ 1C cycling performance of (SO4)3 / C composite cathode material.

[0025] Figure 6 is Na in Example 1 2+2δ Fe 2-δ 10C long cycle performance of (SO4)3 / C composite cathode material.

[0026] Figure 7 is Na in Example 1 2+2δ Fe 2-δ High and low temperature 1C cycling performance of (SO4)3 / C composite cathode materials DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with specific embodiments.

[0028] Example 1

[0029] Step 1: Preparation of a crystal water-free precursor composite material

[0030] Sodium sulfate, ferrous sulfate and ascorbic acid were added to deionized water in a molar ratio of 20:20:1, and stirred continuously to completely dissolve them to obtain an aqueous solution in which the solutes were evenly dispersed. Then, 5 wt.% carbon nanotubes were added and ultrasonically dispersed to obtain a black suspension, which was vacuum dried at 150°C for 12 hours to obtain a Na2Fe(SO4)2 precursor material without crystal water.

[0031] Step 2: Preparation of sodium iron sulfate composite positive electrode material

[0032] The precursor without crystal water was sintered at 400 °C for 10 h in a tube furnace with argon atmosphere and then cooled to room temperature to obtain Na 2+2δ Fe 2-δ (SO4)3 / C composite positive electrode material.

[0033] Figure 1 The X-ray diffraction pattern of the Na2Fe(SO4)2 precursor composite material without crystalline water prepared in Example 1 shows that the XRD diffraction peak intensity is high and the half-peak width is narrow, indicating that the Na2Fe(SO4)2 precursor material has a high degree of crystallinity.

[0034] Figure 2 This is the TG-DSC graph of the Na2Fe(SO4)2 precursor composite material without crystal water prepared in Example 1. Unlike the Na2Fe(SO4)2·4H2O hydrated precursor, which undergoes obvious mass loss when heated at 150-250°C, the TG-DSC curve of the Na2Fe(SO4)2 precursor material without crystal water prepared by the present invention shows that it has almost no mass change when heated at 150-400°C, further confirming the absence of crystal water in its crystal structure.

[0035] Figure 3 The improved conductive Na prepared in Example 1 2+2δ Fe 2-δ The X-ray diffraction pattern of the (SO4)3 / C composite cathode material shows that the XRD diffraction intensity is high and the half-peak width is narrow, indicating that the material has a high degree of crystallinity. Further matching the position and number of the main diffraction peaks, it can be determined that the main phase is Na 2+2δ Fe 2-δ (SO4)3 and a small amount of impurity phase Na6Fe(SO4)4.

[0036] Figure 4 The improved conductivity Na 2+2δ Fe 2-δ From the scanning electron microscope image of the (SO4)3 / C composite positive electrode material, it can be observed that the material has a rich pore structure, which provides channels for the infiltration and penetration of the electrolyte, and is beneficial to the diffusion of sodium ions from the active particles to the electrolyte; in addition, exposed carbon nanotubes are observed on the surface of the particles, which provide channels for high-speed transmission of electrons between particles during the charge and discharge process, enabling the battery to exert high rate capacity and high capacity retention rate in a wide temperature range.

[0037] Figure 5 The improved conductive Na prepared in Example 1 2+2δ Fe 2-δThe 1C cycle performance diagram of the (SO4)3 / C composite positive electrode material shows that its first-cycle discharge capacity is about 64 mAh / g, and its capacity retention rate is about 92% after 200 cycles.

[0038] Figure 6 The improved conductive Na prepared in Example 1 2+2δ Fe 2-δ The 10C long cycle performance diagram of the (SO4)3 / C composite positive electrode material shows that the first cycle discharge capacity is about 54mAh / g, and the capacity retention rate is about 92% after 1000 cycles.

[0039] Figure 7 The improved conductive Na prepared in Example 1 2+2δ Fe 2-δ The high and low temperature 1C cycle performance diagrams of the (SO4)3 / C composite positive electrode material show that the capacity retention rate exceeds 90% after 100 cycles of high and low temperature cycling, especially at a low temperature of -25°C, there is almost no capacity attenuation after 100 cycles.

[0040] Example 2

[0041] Step 1: Preparation of a crystal water-free precursor composite material

[0042] Sodium sulfate, ferrous sulfate and ascorbic acid were added to deionized water in a molar ratio of 20:20:1, and stirred continuously to completely dissolve them to obtain an aqueous solution in which the solutes were evenly dispersed. Then, 1wt.% carbon nanotubes were added and ultrasonically dispersed to obtain a black suspension, which was vacuum dried at 150°C for 12h to obtain a Na2Fe(SO4)2 precursor composite material without crystal water.

[0043] Step 2: Preparation of sodium iron sulfate composite positive electrode material

[0044] The precursor without crystal water was sintered at 400 °C for 10 h in a tube furnace with argon atmosphere and then cooled to room temperature to obtain Na 2+2δ Fe 2-δ (SO4)3 / C composite positive electrode material.

[0045] Example 3

[0046] Step 1: Preparation of a crystal water-free precursor composite material

[0047] Sodium sulfate, ferrous sulfate and ascorbic acid were added to deionized water in a molar ratio of 20:20:1, and stirred continuously to completely dissolve them to obtain an aqueous solution in which the solutes were uniformly dispersed. Then, 10 wt.% carbon nanotubes were added and ultrasonically dispersed to obtain a black suspension, which was vacuum dried at 150°C for 12 hours to obtain a Na2Fe(SO4)2 precursor composite material without crystal water.

[0048] Step 2: Preparation of sodium iron sulfate composite positive electrode material

[0049] The precursor without crystal water was sintered at 400 °C for 10 h in a tube furnace with argon atmosphere and then cooled to room temperature to obtain Na 2+2δ Fe 2-δ (SO4)3 / C composite positive electrode material.

[0050] Comparative Example 1

[0051] Step 1: Preparation of hydrated precursor composite material

[0052] Sodium sulfate, ferrous sulfate and ascorbic acid were added to deionized water at a molar ratio of 20:20:1, and stirred continuously to completely dissolve them to obtain an aqueous solution in which the solutes were uniformly dispersed. Then, 5 wt.% carbon nanotubes were added and uniformly dispersed by ultrasonication to obtain a black suspension, which was dried in air at 150°C for 12 hours to obtain a hydrated Na2Fe(SO4)2·4H2O precursor composite material.

[0053] Step 2: Na 2+2δ Fe 2-δ Preparation of (SO4)3-H Composite Cathode Materials

[0054] The hydrated Na2Fe(SO4)2·4H2O precursor composite material was sintered at 400℃ for 10h in a tube furnace with argon atmosphere and then cooled to room temperature to obtain Na 2+2δ Fe 2-δ (SO4)3-H composite positive electrode material.

[0055] Comparative Example 2

[0056] Step 1: Preparation of crystal water-free precursor material

[0057] Sodium sulfate, ferrous sulfate and ascorbic acid were added to deionized water at a molar ratio of 20:20:1, and stirred continuously to completely dissolve them to obtain an aqueous solution in which the solutes were evenly dispersed. The aqueous solution was then vacuum dried at 150°C for 12 hours to obtain a Na2Fe(SO4)2 precursor material without crystal water.

[0058] Step 2: Na 2+2δ Fe 2-δ Preparation of (SO4)3 cathode materials

[0059] The precursor without crystal water was sintered at 400 °C for 10 h in a tube furnace with argon atmosphere and then cooled to room temperature to obtain Na 2+2δ Fe 2-δ (SO4)3 positive electrode material.

[0060] Test experiment

[0061] The positive electrode material, conductive carbon black and binder were weighed and ground in a ball mill according to a mass fraction ratio of 70:20:10, and then the evenly ground slurry was scraped onto the aluminum foil current collector. After vacuum drying overnight, it was rolled and cut to obtain the positive electrode sheet. In a glove box filled with argon (water and oxygen content were both less than 0.1ppm), metallic sodium was used as the negative electrode and glass fiber filter paper as the diaphragm. After assembling in the order of positive electrode, diaphragm and negative electrode, an appropriate amount of electrolyte (1M NaClO4 EC:PC=1:1 and 5vol%FEC) was injected and sealed to obtain a sodium ion battery, and the battery was subjected to stability tests of 1C cycle 200 weeks and 10C long cycle 1000 weeks at room temperature.

[0062] Table 1 shows the room temperature battery performance test data of all recorded Examples 1-3 and Comparative Examples 1-2

[0063]

[0064] In addition, the cycle stability of the composite cathode material prepared in Example 1 at a high temperature of 60° C. and a low temperature of −25° C. was tested respectively.

[0065] Table 2 shows the test data of high temperature discharge and low temperature discharge performance of the battery in Example 1.

[0066]

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same; although the present invention has been described in detail with reference to the above embodiments.

[0068] Those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery, characterized in that: The sodium iron sulfate composite positive electrode material can be obtained by calcining a composite precursor without crystal water under an inert atmosphere.

2. A process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery, characterized in that: The crystal water-free precursor composite material can be obtained by vacuum drying a uniform suspension containing sodium sulfate, ferrous sulfate, ascorbic acid and carbon nanotubes.

3. The process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery according to claim 1, characterized in that: The molar ratio of the iron salt to ascorbic acid is 20 to 80:

1.

4. The process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery according to claim 1, characterized in that: The material drying and crystallization process is a vacuum condition, the vacuum drying temperature is 100-150°C, and the drying time is 12-24h.

5. The process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery according to claim 1, characterized in that: The added amount of the carbon nanotubes is 1-10 wt.%.

6. The process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery according to claim 2, characterized in that: The inert atmosphere is at least one of Ar, N2, and Ar+H2.

7. The process for preparing a sodium iron sulfate composite positive electrode material from a crystal water-free precursor and a sodium ion battery according to claim 2, characterized in that: The sintering temperature is 350-450° C., and the sintering time is 6-12 hours.

8. A sodium ion battery, characterized in that: The positive electrode material of the battery is a sodium iron sulfate composite positive electrode material prepared from a crystal water-free precursor as described in any one of claims 1 to 7.

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